Databases

• Author: Dorothy Maxwell, Gary Hansen
• Pages: 189-192

Page 189

Databases are designed to manipulate large amounts of information by inputting, storing, retrieving, and managing that information. Databases use a table format, with Microsoft Access being one of the most widely used.

Databases consist of rows and columns. Each piece of information is entered into a row, which creates a "record." Databases are commonly used when saving addresses or other types of long lists of information. Once the records are created in the database, they can be sorted and manipulated in a variety of ways that are limited primarily by the software being used.

The word data is normally defined as facts from which information can be derived. For example, "Fred Crouse lives at 2209 Maple Avenue" is a fact. A database may contain millions of such facts. From these facts the database management system (DBMS) can derive information in the form of answers to questions such as "How many people live on Maple Avenue?" The popularity of databases in business is a direct result of the power of DBMSs in deriving valuable business information from large collections of data.

Databases are somewhat similar to spreadsheets, but databases are more powerful than spreadsheets because of their ability to manipulate the data. It is possible to do a number of functions with a database that would be more difficult to do with a spreadsheet. Consider these actions that are possible to do with a database:

Perform a variety of cross-referencing activities

Complete complicated calculations

Bring current records up to date

Retrieve large amounts of information that match certain criteria

RELATIONAL DATABASES

Most modern databases are relational, meaning that data are stored in tables, consisting of rows and columns, and that data in different tables are related by the meanings of certain common columns. (The tables in a database are sometimes called files, the rows are called records, and the columns are called fields. Nevertheless, this is an older terminology, left over from the early days of business computer systems.) The following is an example of a simple relational database consisting of three tables: one for customers, one for products, and one for sales:

Page 190

Customers
customer_no	name	address	phone
1001	Jones	320 Main	555-8811
1002	Smith	401 Oak	555-8822
1003	Brown	211 Elm	555-8833
1004	Green	899 Maple	555-8844
Products
product_no	description	price
25	Ring	3.25
33	Gasket	1.23
45	Shaft	4.55
Sales
sale_no	date	customer_no	product_no
841	3/11	1002	45
842	3/12	1001	25
843	3/12	1002	45
844	3/13	1004	33
845	3/14	1003	25
846	3/15	1002	33

Suppose one wants to know the customer's name for sale number 845. Looking in the customer number column of the Sales table, one will see that it was customer 1003. Next, one refers to the Customers table and finds customer 1003. Here one see the customer's name is Brown. So, Brown was the customer for sale number 845.

STRUCTURED QUERY LANGUAGE

The foregoing is a simple example of a database query. In a modern database, queries are expressed in a query language, which requires a particular format that can be recognized and interpreted by the DBMS. The standard query language for relational databases, as adopted by the American National Standards...